The meaning is that when the flame moves because of the
breeze, Mirza Sahib's 'delicacy
of thought' has declared it to be due to weakness. Addressing the Flame
has created in the verse an extraordinary pleasure. (123)

He addresses the Flame: from your flickering the sacret
was revealed, that the candle has become weak. And this weakness is out of
grief that its lover (the Moth) has been burnt up. The flame flickers from
the breeze, but the poetic cause [shaa((iraanah taujiih]
is this....

Janab [Nazm] Tabataba'i has declared the address to the Flame
to be unpleasing. But he has not written any reason. In my opinion, to address
a lifeless thing like a living one is a thing of great pleasure. (159)

This would be an excellent verse for performance in a mushairah.
If we heard the first line alone, we'd have no idea who the us
was who felt the grief, or why a 'Flame' was being addressed. Only the second
line makes the first intelligible, and even then the crucial word, 'weakness', is deferred
as long as possible in that line, so that revelation comes all at once, with
a real burst of pleasure.

This verse also makes clear how seriously the other
commentators take the pronouncements of Nazm. Often they simply adopt his
views, but when he says something unduly critical they tend to react strongly.
His declaring the vocative to the Flame unpleasing causes Bekhud Dihlavi to
pointedly say the opposite, and Bekhud Mohani to disagree with him in so many
words. That's one reason (though not the only one of course) that I give such
prominence to Nazm in this project.

Although the commentators don't use the term 'elegance in assigning a cause', that's certainly what the two Bekhuds are describing.
We might wrongly have thought it was the breeze, but now we know the real reason why the candle flame flickers. Its weakness has not physical causes,
but emotional ones-- it's trembling with sorrow and sympathy over the (vain)
longings of the Moth.

Which of course is a bit unorthodox. We know that the candle
is the Moth's beloved, and that the moth will sooner or later die a fiery,
ecstatic death in the flame. Since when does the beloved go all 'weak' with
sympathy, to the point of trembling, over the sufferings of the lover? This
is almost un-ghazal-like behavior; the beloved's proper, necessary role is to
be cold, fickle, unavailable. Perhaps that's why Ghalib describes such a show of sympathy as 'weakness'; the tone might almost be a bit scornful. But after all, if the beloved is sufficiently fickle, once in a while she can
inadvertently happen to be kind; candles are made of wax, so perhaps they
can't quite manage to have hearts of stone.